1. Field of the Invention
The present invention relates to an ink jet printer in which ink is ejected by piezoelectric elements.
2. Description of the Related Art
Ink jet printers in which ink is ejected by piezoelectric elements are widely used in copiers, facsimiles, computers, word processors and compound machines including these functions. A conventional ink jet printer includes a pressure chamber plate, a piezoelectric member, and a vibrating plate arranged between the pressure chamber plate and the piezoelectric member. The ink jet printer further includes a nozzle plate having nozzles communicating with the pressure chambers of the pressure chamber plate.
The pressure chamber plate includes a plurality of pressure chambers separated by bulkheads. The piezoelectric member is formed as a block having drive sections separated by parallelly extending grooves and bulkhead support portions. The drive sections are arranged opposite to the pressure chambers, and the bulkhead support portions are arranged opposite to the bulkheads. Inner electrodes are arranged in the piezoelectric member to cause the drive section to extend and contract for ejecting ink.
One group of inner electrodes (positive electrodes) extend from an end surface of the piezoelectric member to the inside of the piezoelectric member, and the other group of inner electrodes (negative electrodes) extend from an opposite end surface of the piezoelectric member to the inside of the piezoelectric member. These electrodes overlap each other within the piezoelectric member and can supply a voltage to the drive sections of the piezoelectric member so that the drive sections can be extended and contracted. When the drive section is extended, the volume of the pressure chamber opposite to the drive section is reduced, so that ink can be ejected from the pressure chamber.
Japanese Unexamined Patent Publication No. 6-316071 discloses an ink jet printer which includes a piezoelectric member having vertical walls separated by a plurality of grooves and a cover plate that covers the piezoelectric member. In this the prior art, the grooves sectioned by the vertical walls and the cover plate function as both ink passages and pressure chambers, so it does not require the pressure chamber plate of the previously described ink jet printer.
Electrodes are formed on both sides of the vertical walls, and when an electric voltage is applied to the electrodes, the vertical walls are extended and contracted in the transverse direction, whereby the volume of the ink passage and pressure chamber, which are formed by the groove, can be changed and ink can be ejected. In this type ink jet printer, the electrodes provided on both sides of the vertical walls can come into contact with ink in the ink passage and pressure chamber. Therefore, a protective film is formed to cover the electrodes, so that the electrodes do not come into direct contact with ink.
In the previously described ink jet printer, the piezoelectric member is isolated from the pressure chamber plate via the vibrating plate. Therefore, ink flows only into the pressure chambers in the pressure chamber plate, and no ink flows to the piezoelectric member. Since the inner electrodes are arranged within the piezoelectric member, it is unnecessary to provide a protective film to cover the inner electrodes to protect the inner electrodes from ink.
However, in this ink jet printer, the inner electrodes are located very close to each other in the piezoelectric member, and the inner electrodes are exposed to the side surfaces of the drive sections of the piezoelectric member due to the manufacturing process. Therefore, it has been found that there is a possibility that the inner electrodes are short-circuited when water or moisture gets into the ink jet printer.